Hollow fiber membrane for filtration of liquids

ABSTRACT

The present invention provides an intrinsically anti-microbial hollow fiber membrane for filtration of liquids. The membrane comprises a plurality of porous hollow bilayer membrane fibers wherein the liquid enters from outside of the fiber, passing through the porous membrane into the lumen of the fiber and coming out from the hollow ending of the fiber, wherein this configuration provides a liquid outside-in arrangement and retains the filtrate outside. It means that membrane of the invention has built in characteristics to act against microbes in order to provide the use with a safe liquid free from microbes. The outer side or outer wall of the hollow fibers may be configured to become hydrophobic whereas inner side or inner wall of the hollow fiber membrane may be configured to become hydrophilic to enhance the water permeability to a great extent. The hollow fiber membrane may be configured to give it an intrinsic anti-microbial capability. A device containing above said membrane has also been disclosed.

This application is a Divisional of U.S. patent application Ser. No.16/400,963, filed May 1, 2019, which claims benefit of PatentApplication No. 319/2018, filed May 3, 2018 in Pakistan, PatentApplication Nos. 1816030.9, filed Oct. 1, 2018 and 1906074.8, filed Aril30, 2019 in Great Britain, which applications are incorporated herein byreference. To the extent appropriate, a claim of priority is made toeach of the above disclosed applications.

FIELD OF INVENTION

The present invention is in the field of liquid filtration, for example,those using hollow fiber membrane modules having intrinsicanti-microbial properties with an outside-in liquid flow configuration.The membrane can find utility in portable water filtration devicesthrough the multipurpose housing that works directly under suctionpressure or passage pressure or gravitational head of liquid. Inparticular, the exemplary embodiments of the present invention alsorelate to the hydrophobic outer side or outer wall of hollow fibers andthe hydrophilic inner wall of the hollow fiber membrane having excellentwater permeation performance for a prolonged period of time without anybackwashing.

BACKGROUND OF INVENTION

Pure drinking water has always been a big issue for people all aroundthe globe. 663 million people rely on unimproved water sources,including 160 million people depending on surface water. Globally, atleast 2.1 billion people use a drinking-water source contaminated withfeces. Contaminated water can transmit diseases such as diarrhea,cholera, dysentery, typhoid, and polio. Some 842,000 people areestimated to die each year from diarrhea because of unsafe drinkingwater, sanitation and hand hygiene. Diarrhea is largely preventable, andthe deaths of 361,000 children aged under 5 each year could be avoidedeach year if these risk factors were addressed. Almost 240 millionpeople are affected by schistosomiasis an acute and chronic diseasecaused by parasitic worms contracted through exposure to infested wateras per WHO reports.

In Pakistan, 44% of the population has complete inaccessibility to puredrinking water throughout their lives. In 2015, 311 children died onlyin Thar due to the scarcity of clean water. In Khyber Pakhtunkhwa (KPK)and the Federally Administered Tribal Areas (FATA), 40% of deaths occurdue to water-borne diseases. Every minute, a child dies in Pakistan dueto contaminated water. 1 million Diarrhea cases are reported every yearin Pakistan. Pakistan is currently spending 1.3 billion dollars onwaterborne disease elimination every year. Per WHO, 25-30% of Pakistanisadmitted to hospitals are due to waterborne bacteria and 60% of totalinfant deaths are due to contaminated water.

Clean water is a big problem at household as well as individual level.For people on the move, clean drinking water has become an expensiveresource. A requirement of a device that can filter any available wateron-the-spot is the need of the time. On average, more than 70% of freshavailable water is contaminated and hence not safe to drink. The currenttechnologies used are either expensive, not-portable, require power orare short-lived.

During natural or other disasters, emergency, or major incidents, therescue departments or military use either disinfectant medicines,coagulant tablets, or if possible, they install a water filtrationplant. The first two are inefficient and unreliable as they have knownharmful effects on the human body, whereas the last one is expensive andclean water transportation is difficult as well.

The conventional water filtration membranes require power to pump waterthrough the membrane. These membranes have undefined or larger poresizes, which normally results in the escape of biological contaminationinto the purified water side of the membrane. Hence, most of theconventional membrane-based water filtration solutions are eitherequipped with UV light, Ozonation or Chlorination units (disinfectants).The prior two require high energy whereas the last one has carcinogeniceffects on humans.

Filters based on sand/granite/charcoal/adsorbents beds have lowprocessing speed, are heavy in weight, have a low processing capacity,and low level of efficiency in removal of biological contamination(especially viruses). In order to provide filtered water on a massscale, a large setup is required and a frequent change of adsorbent isrequired to maintain filtration speed. A post-processing unit is alsorequired to remove biological contamination in this case.

The ceramic membranes now used in portable water filtrations units lackdurability. They are prone to damage when they face an impact, areheavier in weight, and require high temperatures for manufacturing. Itis also difficult to maintain a pore size in such membranes that canremove biological contamination efficiently. The sintering process usedto produce such ceramics is not commercially well established to reducepore size below 20 nm.

Hollow fiber membranes are widely employed in the domestic andindustrial sector for the microfiltration and ultrafiltrationapplications. During the passage of water from one side of the membraneto the other, filtration process occurs by selectively allowing only thewater molecules and those particles which are considerably smaller thanthe surface pore size of the membrane. Hence, the surface of themembranes specifically and the whole fiber thickness, in general, form aboundary which is separating the unfiltered water from the filteredwater. Polyethylene, cellulose acetate, polysulfone, polyvinylidenefluoride, polycarbonate, polyacrylonitrile, etc. are used as materialsfor forming the fibers of the membranes. This method requires that theporous hollow fibers have high porosity and narrow pore sizedistribution to improve separation efficiency and separation accuracy.Moreover, it also required that the membranes possess a pore size thatis most suitable for separation targets, and the characteristics ofeffectively excluding bacteria, suspension solids, and turbidcomponents. Meanwhile, the fibers of the membranes shall have highermechanical strength and high water flux such that they can sustainlong-term use under conditions required for chemically cleaning pollutedmembranes and for high operational pressures. Since such conventionalhollow fiber membranes made of these materials have been developed andused for the purpose of improving filtration performance, certaininadequacies have been identified. For example, these conventionalhollow fiber membranes provide only a low-level processing performance,need backwashing and may get contaminated with bacteria and othermicroorganisms.

Various failed attempts have been made for a solution to these problems,including suggestions to increase porosity. Thus, hollow fiber membranesthat provide a well-balanced water permeation performance with microbiocidal properties and with a long life have not yet been obtained.

Currently, the following three filtration techniques are used in thewater filtration industry: I) Ultrafiltration (UF) 2) Nano Filtration 3)Reverse Osmosis Filtration. Most commonly, for freshwater resources, UFmembranes are in use. The currently available hollow fiber basedportable liquid filtration membranes are based on UF technology andhence, cannot efficiently remove dissolved metals such as Arsenic,chromium, Iron, etc. In order to achieve the removal of these metals, apore size below 2 nm is required.

On the other hand, whilst a method of increasing the pore diameter of amembrane is generally employed for improving the water permeationperformance of a membrane, this increase in pore diameter generallycauses a deterioration in the fractionation performance of the membraneand in the strength of the membrane.

Hollow fiber membrane modules are commonly used for microfiltration andultrafiltration of water, such modules being used in various scales;from large commercial scale plants to portable water filters. One of theknown hollow fiber module configurations for water filters is disclosedin U.S. Pat. No. 4,435,289, where porous hollow fibers are sealed usinghardened resin located at both ends of the fibers which also act assupport. Water enters the fibers from the openings at the supported endsinto the inner volume and is filtered when it passes through the micropores of the hollow fiber walls. This is an inside-out flow, where theclean water moves out from the lumen of the fibers and the filtrateaccumulates on the inner side of the fibers. Such fibers are cleaned byforwarding flushing water through the inner volume of the fibers,possibly combined with a backflush as disclosed in WO 2008/101172 byVestergaard Frandsen.

This principle is also explained with a concept of personal drinkingstraws, such as in EP 22355 02B 1. This device contains a mouthpieceused for suction of water through the straw containing a bundle ofU-shaped hollow fibers with microporous membrane walls, which aresupported with both ends sealed in a head just below the mouthpiece.When the human mouth creates the suction, the flow is from outside toinside. The filtrate remains outside the membrane walls, and clean waterenters the inner volume of the fibers through microporous walls. Thisclean water is then released from the sealed ends near the mouthpiecefor drinking purpose.

This device disclosed in EP 2235502B 1 faces a general problemencountered with such filters; that is, the hollow fibers are made of ahydrophilic material able to transport water efficiently through themembranes and to which a non-slippery water layer is formed on themembranes. Due to this phenomenon, the air cannot, or only hardly can,travel across the membrane walls when these membranes are wet (i.e. whenthey are being used to filter water). This results in a risk of airtrapping in the volume around the fibers, which decreases the waterflow, as the trapped air prevents an efficient water flow through themembranes. Due to this, a higher suction pressure is required by a humanto obtain an optimum flow from the modules.

This problem is very common in such filtration devices and solutions tothis problem have been proposed earlier, as disclosed in theabove-mentioned U.S. Pat. No. 4,636,307 several hydrophobic fibers areadded in the module to repel water that forms a non-slippery layeraround the fibers and prevent the air passage. However, with respect toproduction, this solution is complicated and expensive.

Another configuration instead of using a U-shaped hollow fiber membranemodule, uses a module that extends into an upstream chamber, the fibershave an open end supported and sealed in a head and are closed andextending into an upstream water chamber, as disclosed in EP 0938367 andas also mentioned in EP 2235502B 1. The principle is analogous to theone just described and encounters the same problem.

A different form of configuration is disclosed in US 2004/078625, wheretwo U-shaped membrane modules are housed in a single pipe and the bentarc parts facing each other. The water flows inside-out from the firstmodule whose open ends are supported and sealed at the suction piece ofthe straw. The clean water enters the chamber between two modules andthen flows outside-in from the second U-shaped module whose open endsare supported and sealed near the mouthpiece. This system is prone toair accumulation in the chamber between the two modules which can resultin reduced water flow rate or higher requirement of suction pressure.

In contrast to the above configuration, a method is disclosed in U.S.Pat. No. 8,852,439 B2, where a single U-shaped hollow fiber module isused in order to avoid air trapping with all hydrophilic fibers. Theopen ends are supported and scaled near the suction piece and the bentfaces the mouthpiece. This is reversely configured compared to EP2235502 B 1. This configuration is claimed to have a reduced risk of airtrapping as the volume inside the fibers is much smaller than the volumeof the compartment. The water follows an inside-out flow pattern. Thecleaning of the accumulated filtrate is done by blowing air from themouth which results in backflushing.

The inside-out flow through the hollow fiber membrane as disclosed inU.S. Pat. No. 8,852,439 B2 causes the coarse particles to get stuckinside the hollow fibers of the membrane. These particles increase therequirement of suction pressure or passage pressure or gravitationalhead with time and use. This extra suction pressure or passage pressureor gravitational head along with stuck coarse particles causes cracks inthe fiber walls.

These hollow fiber membrane-based filters face a common problem.Bacteria enter the filter body and hollow fibers, for example when airis blown from the mouth for backflushing, when back-washing occurs usingan external component, by exposure of the clean side to bacteria, due topoor sanitation, or due to an unclean environment. These bacteria stickwith the walls and fibers and start to grow in colonies. These bacterialcolonies grow on the filtered water side of the membrane as air is blownthrough mouthpiece of the filter or by back-washing using externalcomponent or by exposure of clean side to bacteria or due to poorsanitation or due to an unclean environment. This results incontamination of filtered liquid, and hence a failure to filter.

In order to tackle this problem, a method is disclosed in U.S. Pat. No.8,852,439 B2. A bacteriostatic/biocidal layer is applied in the innerwalls of the filter so the bacteria do not grow and hence the filteredwater is not contaminated. However, the problem is that this biocidallayer is only applied to filter housing (i.e. inner walls of filterbody) and not on the membrane. Due to this, the membrane is prone tocontamination (on the clean side). Also, this biocidal layer leaches outwith erosion and hence migrates with the filtered liquid. This reducesthe life of antimicrobial functionality. Biocidal materials (if leachedout in outlet/filtered water) are known to have harmful effects onhumans when ingested.

Another method used to mitigate the risk of bacterial growth inside thefilter (e.g. due to backflushing or the exposure of clean side tobacteria or exposure to unclean environment/poor sanitation) is the useof silver Nanoparticles. Silver is an anti-microbial metal as it kills99% of the microbes. Silver Nanoparticles leach out with time leavinglarger cavities in the membrane walls which causes microbial slippage.Due to the migration of Nano silver particles, the anti-microbial effectalso diminishes with time. (See U.S. Pat. Nos. 7,390,343 and 9,200,086).

In all above filtration devices, the porosity of the hollow fibers is upto 80% and so high suction pressure or passage pressure or agravitational head is required to filter liquid, as well as air trappingbecomes a concern.

SUMMARY OF THE INVENTION

It is, therefore, an object the present invention to improve the qualityof filtration by introducing novel intrinsic anti-microbialcharacteristics to a membrane. Optionally, other objectives may beachieved by the present invention, for example increasing the water fluxso that air trapping is no more a problem and clogging of the membraneholes via air bubbles is reduced to the minimum extent; to reduce thesuction pressure or passage pressure or gravitational head requirementof the hollow fibers for water filtration. In particular, the aim of theinvention is to achieve better quality filtered water with a higher flowrate and lesser suction pressure or passage pressure or gravitationalhead.

The inventors have surprisingly found that one can provide a novelmembrane which has inherent antimicrobial properties. This can be usedin multiple purpose portable housings with multiple openings whereinliquids, such as water, flows outside-in through membrane fibers. Itmeans that the membrane of the invention has built-in characteristics toact against microbes in order to provide a safe liquid, such as water,free from microbes.

Another object of the present invention is to provide a method forproducing such a hollow fiber membrane, such a membrane may have a highlevel of strength and excellent in fractionation performance and waterand other liquids permeation performance.

Accordingly, in a first aspect of the present invention, there isprovided an intrinsically anti-microbial hollow fiber membrane forfiltration of liquids comprising a plurality of porous hollow membranefibers wherein the liquid enters from outside of the fiber membrane andpasses through the porous membrane into and along the lumen of thefibers, thereby retaining the filtrate outside of the membrane andfiltered liquid flows out from the hollow end of the fiber.

The hollow fiber membrane of the present invention may be characterizedin that the outer surface or outer wall of the hollow fiber hashydrophobic characteristics whereas the inner surface or inner wall ofmembrane possess hydrophilic characteristics.

The hollow fiber membrane of the present invention may have a pore sizerange from 0.1 nano meter to 25 nano meter.

The hollow fiber membrane may have a fiber diameter ranging from 0.2 mmto 0.6 mm.

The hollow fiber membrane may have a wall thickness from 1 mm to 2 mm.

The hollow fiber membrane of the present invention may be characterizedin that the outer surface or outer wall of the hollow fiber hashydrophobic characteristics whereas inner surface or inner wall ofmembrane possess hydrophilic characteristics having pore size range from0.1 nano meter to 25 nano meter with fiber diameter ranging from 0.2 mmto 0.6 mm and wall thickness equal to 1 mm to 2 mm.

The hollow fibers may be formed from a polymer, optionally athermosetting polymer. For example, the fibers may be formed frompolysulfone polymers, polyethersulfone, polyvinylidene fluoridepolymers, polyacrylonitrile polymers, polymethacrylic acid polymers,polyamide polymers, polyimide polymers, polyether imide polymers, andcellulose acetate polymers, or mixtures thereof. Optionally the fibersmay be formed form aromatic polysulfones, polyacrylonitrile copolymers,polyvinylidene fluoride, and aromatic polyetherimides, or mixturesthereof. The inventors have found that the choice of polymers, andpolymer mixes, can influence the pore formation and so the Pure WaterPermeability (PWP) and Critical Water Flux (CWF). The formation of alarge number of pores over a given area of fiber wall, and so a large %void by volume of the fiber wall, can be achieved by selection ofpolymers to construct the fibers. For example, the fibers comprise orconsist of from 16% to 25% by weight, polyethersulfone, of from 5 to 20%by weight polyvinylpyrrolidone, of from 70% to 90% by weight, N-methylpyrrolidone solution and of from 10% to 45% by weight polyethyleneglycol. Optionally the fibers also comprise polycarbonates, polyamides,and aqueous isopropyl or any combination thereof. For example, thefibers comprise or consist of from 10%-25% by weight polysulfone andfrom 5% to 15% by weight polyvinyl pyrrolidone. For example, the fiberscomprise or consist of from 3%-25% by weight polyethersulfone and from5% to 15% by weight polyvinylpyrrolidone.

The fibers may comprise or consist of polyethersulfone, optionallyUltrason® polyethersulfon, optionally grade 6020p. For example, thefibers comprise or consist of from 12% to 25%, polyethersulfone, of from40% to 85%, N-methyl pyrrolidone and of from 10% to 45% polyethyleneglycol. Such a formulation may also include lithium chloride (optionallyof from 0.3 to 1.5%).

The fibers may be provided in a number of confirmations. For example,the fibers may form a one-layer membrane, the fibers may form a membranecomprising more than one layer, the fibers may form a membrane that is adouble layer (for example, involving two u-shaped sets of fibersprovided opposed to each other within a closed system).

The multiple layers may permit different characteristics to be presentedfrom each layer.

A single layer membrane can be either hydrophobic or hydrophilic. Adouble layer membrane can be either hydrophobic or hydrophilic. Theouter side or wall of the membrane layer (ie the side facing the liquidto be filtered) can be hydrophobic and the inner side layer or wall (iethe side facing the lumen of each fiber and containing filtered liquid)is hydrophilic. The hydrophobic layer reduces the requirement of airtrappings and suction pressure. The hydrophobic layer increases theliquid flux.

The hydrophilic layer allows maintenance of capillary action of theliquid through the pores on fiber walls towards the hollow cavity offibers and decreases the requirement of suction pressure or passagepressure or gravitational head.

The liquid may flow with outside-in orientation (ie liquid to befiltered is provided outside of the fiber lumen, passing inside of thelumen when being filtered). Alternatively, the liquid may flow withinside-out orientation.

In an outside-in orientation, the filtrate is retained outside of themembrane.

For ease of maintenance, the membrane may be washable.

The fibers that define the membrane have pores in their walls throughwhich water can pass. The multiple pores can result in a fiber beingformed that has a void range of from 70 to 90% or 80% to 90% void byvolume of fiber wall. The pore size can range from 0.1 nm to 25 nm indiameter. For usage under suction, the pore size can range from 50 nm to150 nm in diameter. The combination of porosities used in this inventionunique because by doing so the mechanical strength of the fiber is notcompromised, which becomes a concern when higher porosities are achievedin order to achieve higher fluxes.

The fibers of the membrane of the present invention may have a PWP (PureWater Permeation) of greater than 1800 Lmh (Liters per meter square areaof membrane per hour under one bar pressure) and/or a CWF (CriticalWater Flux) of greater than 900 Lmh.

The hollow fibers can form a U-shaped membrane module with open endswhere liquid entered in the membrane for filtration and filtered liquidcomes out through the open ends of fibers. For example, as described inU.S. Pat. No. 5,160,673.

The fibers are preferably intrinsically antimicrobial in nature. Thismeans that they are not simply coated with an antimicrobial substance.As a result, the antimicrobial nature of the membrane does not easilybecome dislodged to be ingested by the user. This may be achieved by anantimicrobial substance being embedded within the polymer system thatforms the fibers. The antimicrobial substance may be embedded by beingphysically trapped within the cross-linking between the polymericchains. The antimicrobial substance may be chemically bonded within thecross-linked polymeric chains. The embedding of the antimicrobialsubstance within the polymer results in the formation of antimicrobialsubstance embedded polymer.

The antimicrobial substance may be metal, metal salt or a metal oxidehaving antimicrobial properties. For example, the substance may be zincoxide, zinc or zinc salt. Thus, as an example, the fibers of the presentinvention may be rendered intrinsically antibacterial by adding at leastone zinc salt to a solution or dispersion, in an aqueous or organicsolvent, of the monomers used to synthesize the polymer that forms thefiber. Alternatively, at least one antimicrobial substance (eg a zincsalt) can be added during the reaction of polymerization of the startingmonomers.

When a zinc salt is used to modify the polymer in order to render itintrinsically antibacterial, the salt may comprise or consist of any oneor combination of PCA (zinc salt of pyrrolidone carboxylic acid), zincoxide, zinc hydroxide, zinc pyrrolidone, and zinc pyrithione.

The polymer or polymer mix into which the antimicrobial substance isembedded can be any one or combination of those provided above forforming the fiber. For example, the polymer may be Polyethersulfone, ora polymer mix comprising Polyethersulfone.

The antibacterial polymer of the invention may be characterized in thathas a release of zinc ions that is below the legal limits of 21 ppm.

The antibacterial polymer of the invention is effective for controllingor eliminating the bacterial proliferation of Gram− and Gram+ bacteria,e.g. Escherichia coli (Gram−) and/or Staphylococcus aureus (Gram+).Other examples can be selected from Escherichia coli, Staphylococcusaureus, Pseudomonas aeruginosa, Acinetobacter baum, Ent. bloacae, C.albicans, and Clostridium species, or combinations thereof.

In order to limit the amount of costly antimicrobial substance, and anyresidual loss of antibacterial substance into the filtered water, theentire fiber does not have to be formed form an antimicrobial embeddedpolymer. Substantially all of the externally facing surface of eachfiber may include an anti-microbial substance within the substance ofthe polymer or polymer mix that forms the fiber. The modified polymer ismixed in such a way that 99% of the whole surface area of the membraneis antimicrobial in nature. The mixing is done through a process whichensures that even when in a small amount for instance 2.5 to 3% of themodified polymer is mixed with the rest of the polymeric mixture, 99% ofthe membrane surface area of the newly manufactured/spun membrane holdsproperty of being intrinsically anti-microbial. Hence the fibers areantimicrobial from the outside as well as inside.

The antimicrobial substance may be a metal oxide or metal. It may beparticles of metal or metal oxide. The anti-microbial substance embeddedpolymer or polymer mix may be from 2-5% by weight of the fiber. Thepolymer or polymer mix absent of anti-microbial substance may be from95-98% by weight of the fiber. The polymer or polymer mix with andabsent of the anti-microbial substance may be the same polymer orpolymer mix.

The method of forming such membrane as discussed above can result in theinherent formation of a fiber with the characteristics discussed above.

For example, the inventors have found that one can provide a high % voidvolume in the fiber wall by selecting an appropriate pore former as partof the process of manufacture of the fibers.

Consequently, in a further aspect of the present invention, there isprovided a process of making an intrinsically anti-microbial hollowfiber membrane comprising the steps of:—

a) mixing polymer or a polymer mix with a pore former comprising PEG(Molecular weight-300);

b) passing the mixture produced in step a) through a spinneret togetherwith a non-solvent for the polymers.

The polymers or polymer mix may be selected from any of those proposedfor constructing the fibres in the first aspect of the presentinvention. Consequently, as an example, the fibres may comprise orconsist of from 12% to 25%, polyethersulfone, of from 40% to 90%,N-methyl pyrrolidone and of from 10% to 45% polyethylene glycol. Such aformulation may also include lithium chloride (optionally of from 0.5 to1.5%).

The PEG may be provided in solution; for example an aqueous solution (eg9:1 PEG:Water solution, or +/−10% thereof).

The non-solvent used in step b) may be water.

In addition to optimizing the pore formation, the inventors have foundthat they are able to construct fibers with the antimicrobial propertytowards the external portions of the wall, but still intrinsic to thefibers; thereby conserving the substances used to provide intrinsicantimicrobial properties. Consequently, the method may comprise thesteps of:

a) mixing an antimicrobial substance embedded polymer or antimicrobialsubstance embedded polymer mix, a polymer or a polymer mix absent of anantimicrobial substance, a solvent for both polymers or polymer mixesand a pore former comprising PEG (Molecular weight-300);

b) passing the mixture produced in step a) through a spinneret togetherwith a non-solvent for the polymers.

In yet, a further aspect of the present invention, there is provided aprocess of making an intrinsically anti-microbial hollow fiber membranecomprising the steps of:—

a) mixing an antimicrobial substance embedded polymer or antimicrobialsubstance embedded polymer mix with a polymer or a polymer mix absent ofan antimicrobial substance and with a solvent for both polymers; alongwith other additives such as PEG, LiCl, PVP etc.;b) passing the mixture produced in step a) through a spinneret togetherwith a non-solvent for the polymers.

Step b) for all processes of the present invention may be carried out ata temperature of from 25 to 80° C., or 40 to 60° C., optionally 50° C.(at atmospheric pressure). The spinneret is required to operate at highspeed. For example, it may operate at a speed of from 350 to 600 rpm, orfrom 450 to 550 rpm, optionally 500 rpm.

The polymers are more able to form a solution with the solvent than withthe non-solvent. Consequently, as the solvent and non-solvent come intocontact with each other during step b), the polymers are driven out ofthe solvent and solidify. The rapid solidification of the polymer atspeed whilst being ejected by the spinneret forms pores in the createdfibers. At the same time, the centrifugal forces induced by thespinneret on the forming fibers pulls the polymer with antimicrobialsubstance embedded therein to the outer surface of the forming fiber,this polymer being denser than that with no antimicrobial substance. Inthis way the fiber is formed with pores and with the outer portion ofthe fiber including the predominant amount of polymer with embeddedantimicrobial polymer, the remainder being formed from the polymerabsent from the antimicrobial substance.

This processes for both further aspects of the present invention may beused to form the membrane of the first aspect of the present invention.Consequently, all features of the first aspect of the present inventionmay apply equally to the further aspects of the present invention. Forexample, the antimicrobial substance may be a metal oxide or metal. Theanti-microbial substance embedded polymer or polymer mix may be from2-5% by weight of the total polymers in the mixture formed in step a).

The polymer or a polymer mix absent of an antimicrobial substance mayform from 95-98% by weight of the fiber.

The polymer may comprise or consist of polyethersulfone, optionally. Thesolvent may be N-Methyl-2-pyrrolidone.

The antimicrobial substance embedded polymer may be polyethersulfon (egUltrason® polyethersulfon, optionally grade 6020p) and the polymer or apolymer mix absent of an antimicrobial substance is polyethersulfon (egUltrason® polyethersulfon, optionally grade 6020p), the polymers beingprovided in a 3% to 97% weight ratio.

The polymer or polymer mix with and absent of the anti-microbialsubstance may be the same polymer or polymer mix. The antimicrobialembedded polymer may have metal oxide particles embedded therein throughcross-linking between the polymeric chains.

The membrane may be incorporated into a conventional device for liquidfiltration, for example any of those described in the review of theprior art above.

Accordingly, in yet a further aspect of the present invention, there isprovided a device for liquid filtration comprising a hollow fibermembrane as described in the first aspect of the present inventionwherein the membrane is placed in a housing with at least one feedchannel and at least one drain channel. The membrane may be placed in ahousing with multiple openings for inlet, outlet, and backflush drains.The hydrophilic layer of the membrane maintains a capillary action ofthe liquid through the holes on fiber walls towards the hollow cavity offibers and decreases the requirement of suction pressure or passagepressure or gravitational head.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described, by way of example only, and withreference to the following figures

FIG. 1 depicts hollow fibers (2), fibers ends sealed and potted (3), andpotting module (4).

FIG. 2 depicts nano pores on a fiber wall and through which a liquidenters the lumen of the hollow fiber (1), and hollow fibers (2).

FIG. 3 depicts nano pores on a fiber wall and through which a liquidenters the lumen of the hollow fiber (1), filtered liquid (5), cavitiesin fiber walls (6), hydrophilic layer (7), meeting point of both layers(8), space created between liquid and fiber due to hydrophobic layer(9), coarse particles, impurities, contaminations (10), hydrophobiclayer facing unfiltered liquid (11), and unfiltered liquid (12)

FIG. 4 depicts nano pores on fiber walls through which a liquid isentered (1), hollow fibers (2), fibers ends sealed and potted (3),potting module (4), filtered liquid (5), cavities in fiber walls (6),hydrophilic layer (7), meeting point of both layers (8), space createdbetween liquid and fiber due to hydrophobic layer (9), coarse particles,impurities, contaminations (10), hydrophobic layer facing unfilteredliquid (11), and unfiltered liquid (12).

FIG. 5 depicts ends of hollow fibers from which filtered liquid comesout (13), potting module wall (14), and the sealant between the fiberends (15).

FIG. 6 depicts a SEM Picture of the fiber wall thickness close-up.

FIG. 7 depicts a SEM Picture of the fiber wall thickness in whole crosssection.

FIG. 8 depicts a chart of the water flux over time derived from a studyof 10 membranes made according to the present invention

FIG. 9 depicts the results of an antibacterial study of the fibermaterial of the present invention.

FIG. 10 depicts representation of the Flux behavior of the membranesample-1 corresponding to the data in Table named under column HFMembrane Flux summary, the sample was tested for PWP and CWF, the graphis extracted from for Figure-8 for the purpose of clarity. The graphshows that the initial PWP reading was recorded at 2400 LMH and thennormalizing at 800 LMH.

FIG. 11 depicts representation of the Flux behavior of the membranesample-2 corresponding to the data in Table named under column HFMembrane-2 Flux summary, the sample was tested for PWP and CWF, thegraph is extracted from for Figure-8 for the purpose of clarity. Thegraph shows that the initial PWP reading was recorded around 1800 LMHand then normalizing at a reading a little above 900 LMH.

FIG. 12 depicts representation of the Flux behavior of the membranesample-3 corresponding to the data in Table named under column HFMembrane-3 Flux summary, the sample was tested for PWP and CWF, thegraph is extracted from for Figure-8 for the purpose of clarity. Thegraph shows that the initial PWP reading was recorded at 1900 LMH andthen normalizing at 900 LMH.

FIG. 13 depicts representation of the Flux behavior of the membranesample-4 corresponding to the data in Table named under column HFMembrane-4 Flux summary, the sample was tested for PWP and CWF, thegraph is extracted from for Figure-8 for the purpose of clarity. Thegraph shows that the initial PWP reading was recorded around 1800 LMHand then normalizing at a reading at around 880 LMH.

FIG. 14 depicts representation of the Flux behavior of the membranesample-5 corresponding to the data in Table named under column HFMembrane-5 Flux summary, the sample was tested for PWP and CWF, thegraph is extracted from for Figure-8 for the purpose of clarity. Thegraph shows that the initial PWP reading was recorded around 2200 LMHand then normalizing at a reading a little above 700 LMH.

FIG. 15 depicts representation of the Flux behavior of the membranesample-6 corresponding to the data in Table named under column HFMembrane-6 Flux summary, the sample was tested for PWP and CWF, thegraph is extracted from for Figure-8 for the purpose of clarity. Thegraph shows that the initial PWP reading was recorded around 1800 LMHand then normalizing at a reading around 1000 LMH.

FIG. 16 depicts representation of the Flux behavior of the membranesample-7 corresponding to the data in Table named under column HFMembrane-7 Flux summary, the sample was tested for PWP and CWF, thegraph is extracted from for Figure-8 for the purpose of clarity. Thegraph shows that the initial PWP reading was recorded around 1930 LMHand then normalizing at a reading around 920 LMH.

FIG. 17 depicts representation of the Flux behavior of the membranesample-8 corresponding to the data in Table named under column HFMembrane-8 Flux summary, the sample was tested for PWP and CWF, thegraph is extracted from for Figure-8 for the purpose of clarity. Thegraph shows that the initial PWP reading was recorded around 2100 LMHand then normalizing at a reading around 780 LMH.

FIG. 18 depicts representation of the Flux behavior of the membranesample-9 corresponding to the data in Table named under column HFMembrane-9 Flux summary, the sample was tested for PWP and CWF, thegraph is extracted from for Figure-8 for the purpose of clarity. Thegraph shows that the initial PWP reading was recorded around 2370 LMHand then normalizing at a reading a little above 800 LMH.

FIG. 19 depicts representation of the Flux behavior of the membranesample-10 corresponding to the data in Table named under column HFMembrane-10 Flux summary, the sample was tested for PWP and CWF, thegraph is extracted from for Figure-8 for the purpose of clarity. Thegraph shows that the initial PWP reading was recorded around 1800 LMHand then normalizing at a reading of 900 LMH.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. Theaspects and features of the present invention and methods for achievingthe aspects and features will be apparent by referring to exemplaryembodiments to be described in detail with reference to the accompanyingdrawings. However, the present invention is not limited to the exemplaryembodiments disclosed hereinafter but can be implemented in variousforms. The matters defined in the description, such as the detailedconstruction and elements, are nothing but specific details provided toassist those of ordinary skill in the art in a comprehensiveunderstanding of the invention, and the exemplary embodiments are onlydefined within the scope of the appended claims. In the drawings, sizesand relative sizes of layers and areas may be exaggerated for clarity inexplanation.

The term “on” that is used to designate that an element is on anotherelement located on a different layer or a layer includes both a casewhere an element is located directly on another element or a layer and acase where an element is located on another element via another layer orstill another element. By contrast, the term “directly on” means that anelement is directly on another element or a layer without theintervention of any other element or layer. In the entire description ofthe present invention, the same drawing reference numerals are used forthe same elements across various figures. Also, the term “and/or”includes the respective described items and combinations thereof.

Spatially relative wordings “below”, “beneath”, “lower”, “above”,“upper”, and so forth, as illustrated in the drawings, may be used tofacilitate the description of relationships between an element orconstituent elements and another element or other constituent element.The spatially relative wordings should be understood as wordings thatinclude different directions of the element in use or operation inaddition to the direction illustrated in the drawings.

In the following description of the present invention, an exemplaryembodiment of the present invention will be described with reference toplane views and sectional views which are ideal schematic views. Theform of exemplary views may be modified due to manufacturing techniquesand/or allowable errors. Accordingly, the exemplary embodiments of thepresent invention are not limited to their specified form as illustratedbut include changes in the form being produced according tomanufacturing processes. Accordingly, areas exemplified in the drawingshave rough properties, and the shapes of areas in the drawings are toexemplify specified forms of areas of elements but do not limit thescope of the present invention.

Hereinafter, A representative example of the structure of the hollowfiber filter membrane (hereinafter sometimes referred to as merely“membrane”) of the present invention will be explained referring to theaccompanying drawings. FIG. 1 is an enlarged photograph of a crosssection perpendicular to the lengthwise direction of the membrane, andFIG. 2 is an enlarged photograph of the inner surface of the membrane.

The membrane of the present invention is formed from a number of hollowfibers, each having an inner surface and an outer surface, and comprisesa network structure which integrally continues from one surface (e.g.,the inner surface) to another surface (e.g., the outer surface) as shownin FIG. 3. The network structure in the membrane has no vacant portionsof the polymer such as a finger-shaped structure layer having cavitiesand a void layer.

The membrane of the present invention comprises a network structurehaving an anisotropy in pore diameter, such that the membrane has alayer with a lower average pore diameter of pores present therein(hereinafter referred to as “average pore diameter of the outersurface”) in the outer surface or near the outer surface compared to theaverage pore diameter of pores present in the inner surface of themembrane (hereinafter referred to as “average pore diameter of innersurface”). The pore diameter generally becomes gradually greater towardthe inner surface of the membrane form that towards the outer surface ofthe membrane. According to an embodiment of the invention, it is ensuredthat more than 99% of the pores are of the size of mentioned diameter onthe outer surface (hereinafter referred to as “average pore diameter ofouter surface”).

The membrane of the present invention has a void content of 70-90% whenthe material of the membrane is polyethersulfone and depending on thevoid content, the breaking stress IS in the range of 2 to 3.5-bar andthe breaking elongation is up to 70%.

As materials which constitute the hollow fiber membrane of the presentinvention, mention may be made of, for example, polysulfone polymers,polyethersulfone, polyvinylidene fluoride polymers, polyacrylonitrilepolymers, polymethacrylic acid polymers, polyamide polymers, polyimidepolymers, polyetherimide polymers, and cellulose acetate polymers.Especially preferred are aromatic polysulfones, polyacrylonitrilecopolymers, polyvinylidene fluoride, and aromatic polyetherimides. Atype polyethersulfone is especially preferred.

In a further aspect of the present invention, there is also described afiltering device for liquid filtration comprising a hollow fibermembrane of the invention wherein the membrane is placed in a housingwith at least one feed channel and at least one drain channel. Accordingto the device of the invention, the hydrophilic layer of membranemaintains a capillary action of the liquid through the holes on thefiber walls towards the hollow cavity of fibers and decreases therequirement of suction pressure or passage pressure or gravitationalhead.

The intrinsically anti-microbial hollow fiber membrane is produced byspinning the polymer mixture at high speed revolutions to place the saidpolymer mixture at the circumference of the base polymers, wherein thepolymer mixture comprising of 3% of antimicrobial embeddedpolyethersulfon 6020p in base polyethersulfon that does not include anantimicrobial substance which gives around 99.9% surface area of thefinished product as antimicrobial. As the antimicrobial embedded polymerhas higher density, the centrifugal force pushes it out-wards and placesit at the circumference of the base polymer which reduces the cost ofproduction of a product. The antimicrobial polymer is chemicallydeveloped by embedding the metal oxide particles in polymers throughcross-linking between the polymeric chains. This produces anintrinsically antimicrobial polymer where the susbtances impartingantimicrobial properties never leach out and never migrate from thepolymer to any other substance in contact.

Examples of the present invention will be shown below, but the presentinvention is not limited to these examples. Methods for the measurementof properties are as follows:

The hollow fiber membranes used as samples for measurement are all inthe state of being sufficiently impregnated with water. As for themembrane obtained by using polyvinyl pyrrolidone as an additive, themembrane was dipped in an aqueous sodium hypochlorite solution and thenwashed with hot water to make a membrane in which substantially nopolyvinyl pyrrolidone was present.

Water permeation of the hollow fiber membrane was expressed by theamount of filtered water when ultrafiltration water of 25.degree. C. wasallowed to permeate through a sample of the hollow fiber.

Example 1

Although preferred embodiments of the present invention have beendescribed for illustrative purposes, it will be apparent to thoseskilled in the art that various modifications, additions andsubstitutions can be made in the present invention without departingfrom the spirit or scope of the invention. Thus, it is intended that thepresent invention cover the modifications and variations of thisinvention provided they come within the scope of the appended claims andtheir equivalents.

The device of the present invention is an intrinsic anti-microbialhollow fiber membrane. The membrane received an intrinsic change on amicrometrical scale which results in antiseptic and antibacterialcharacteristics. The adhesion and proliferation of bacteria on thesurface of the object are slowed down and the microbes and bacteriacount is being strongly reduced. This antiseptic/anti-microbial natureof the material is the intrinsic property of the membrane polymer andnever migrates/leaches with filtered liquid and never diminishes withuse/time.

The hollow fiber consists of two layers. The outer layer is hydrophobicand the inner layer is hydrophilic by nature. The hydrophobic layernever allows the water to come in physical contact with membrane hencestops any adherence of any kind on it. Hydrophobic layer makes the airtrappings minimum as the outside-in passage of air is facilitated by theabsence of water layer on the outside hence decreasing the suctionpressure requirement and increasing the flux of liquid. While the innerhydrophilic layer maintains a capillary action of the liquid through theholes on fiber walls towards the hollow cavity of fibers hencedecreasing the requirement of suction pressure or passage pressure orgravitational head. The liquid flows in outside-in orientation i.e.filtration happens when liquid from the outside of the fiber wall passesthrough its hole and filtered liquid comes out of the hollow ending ofthe fiber. Hence keeping the unfiltered liquid outside the fiber wallsand retaining the filtered liquid inside the hollow fiber. Making it theonly membrane used with outside-in direction of flow while having ahydrophobic layer on its outside and a hydrophilic layer on its inside.

Fibers can have pores ranging from 0.1 nm to 25 nm in its walls. Theliquid especially water is filtered when it passes to the hollow cavityof fiber from the holes in its walls from the outside of the fiber. Thefibers make U-shaped membrane modules with open ends sealed andsupported in such a way that U-shaped side always faces the liquidcoming for filtration and filtered liquid always comes out through theopen ends of fibers. The porosity of the fibers ranges from 70% to 90%.

The anti-microbial embedded polymer is developed by chemically bondingmetal oxide particles in polymer ultrason Polyethersulfon (A BASFbrand), which produces an intrinsically antimicrobial polymer in whichthe antimicrobicity never leaches out and never migrates from thepolymer to any other substance come in contact with the surface of thepolymer unlike the existing antimicrobial membranes on whichantimicrobicity has been created by coating the surface with anantimicrobial substance which may leaches out and contaminate thesubstance which comes into contact with it. Polyethersulfon is thepolymer of which the hollow fibers of the membrane are made.

The porosity is achieved during the hollow fiber membrane manufacturingprocess. The process involves the use of 2 tanks connected to thespinneret via gear-pump assisted flow tubes. The dope solution tank andthe bore solution tank. The polymers are mixed with a solvent where theytotally dissolve in the dope solution tank. As soon as the flow of bothdope and bore solution (also called as the non-solvent) starts throughthe spinneret of the spinning machine the process of phase inversionstarts (the polymer that was dissolved in the solvent now will start tosolidify). This phenomenon can be explained by the simple process ofmass-transfer, as soon as the non-solvent and solvent come in contactthe interaction between them acts as the driving force to push thedissolved base polymer out of the solvent and hence it starts tosolidify again. During this process the pores are created because theinstantaneous (very short, takes less than a second) de-mixing the timeperiod too short for the polymer to solidify completely and hence as thepolymer starts to come out of the solvent and solidify, theinstantaneous nature of de-mixing renders some discontinuities in thesolidifying polymeric structure and these discontinuities (spaces) areultimately the pores and all these pores combined to give the porosityto the fiber. The process of fiber formation is carried out at 50degrees Celsius at atmospheric pressure with the spinneret operating at500 rpm. 3% by weight of the total polymer is formed from theantimicrobial embedded polymer, whilst 97% is antimicrobial substanceabsent polymer.

Example 2:—Pore Formation

A dope solution/polymer solution was made by combining the components inthe table below. To this, the below described bore solution/innersolution was added and the combination thoroughly mixed. This mixturewas then passed through a spinneret along with water in order to formhollow fibers.

-   -   1. In the process of making dope solution, low molecular weight        additives (such as LiCl etc) should be added first in the        solvent with constant agitation and at 50° C.    -   2. Gradually, additives with the higher molar masses (such as        PEG, PVP etc) should be introduced into the solvent at constant        stirring.    -   3. Lastly, the base polymer (such as PES, PSU etc.) will be        introduced in the dope solution under the constant stirring and        at 80° C. for approx. three hours.    -   4. Dope solution will only be considered ready for spinning,        until all the additives and the base polymer is homogenously        dissolved in the solvent. The dope solution should be in one        phase before spinning along with the absence of any air bubbles        and foreign particles.    -   5. Dope solution should be left overnight or for sufficient        amount of time, without agitation, in order to remove the air        bubbles, generate during stirring.    -   6. The spinneret temperature should be at room temperature but        the temperature of the coagulant liquid should be at 50° C.    -   7. The bore liquid can be either pure PEG or a mixture of        PEG:Water 9:1 or NMP:Water 9:1.

Dope Solution/Polymer Solution Bore Solution/ (% by volume) InnerSolution Coagulant PES 15% Polyethersulone PEG:Water 100% Water(Ultrason ® E6020P) (9:1) PEG 38% (Polyethylene glycol) LiCl (LithiumChloride) 1.5% H2O 2% NMP (N-methyl-2-Pyrrolidone) 43.5%

It has been found that fibers produced according to the above process,through testing and benchmarking the performance of these fibers, aresuperior as compared to the fibers available currently at disposal orcited in the prior arts. The PWP and CWF values are higher then whatusually are reported for such fibers in the published literature. PWPvalue of 1800 Lmh and CWF value of 900 Lmh for fibers with 20 nm poresize is higher than those compared to the Hollow fiber membranes forultra-filtration.

When PEG is used as the bore solution and as a pore former in the dope,it is believed due to its high viscosity and flowing behavior, it hasbeen observed to impart properties to the nascent fibers in terms ofmorphology. In particular, the fibers tend to have a well pronouncedfinger-like pore structures, hence having straight and well-pronouncedchannels along the thickness of the fiber as seen in the FIG. 6 and FIG.7, the picture of the wall thickness taken with a Scanning ElectronMicroscope (SEM) when the fiber is observed with the instrument with itscross-section facing the observer.

The Pure Water Permeation and Critical Water Flux for the fibers madeaccording to the above method were then established.

Pure Water Permeability (PWP): The pure water permeability, also knownas the pure water flux is defined as the volume of water that passesthrough a membrane per unit time, per unit area and pre-unit oftransmembrane pressure. This property indicates the effort required togenerate permeate for a membrane and can be used to compare the initialperformance of a membrane. This analysis does not, however, provide anyguidance as to the performance of the material for extended periods oftime and so it is also useful to look at Critical Water Flux. (seePersson, Kenneth M., Vassilis Gekas, and Gun Trägårdh. “Study ofmembrane compaction and its influence on ultrafiltration waterpermeability.” Journal of membrane science 100, no. 2 (1995): 155-162.)

Critical Water Flux (CWF): Either as the flux at which the transmembranepressure (TMP) starts to deviate from the pure water line (the strongform of critical flux) or as the first permeate flux for whichirreversible fouling appears on the membrane surface. The critical fluxcan be generally defined as the “first” permeate flux for which foulingbecomes predominant; being then well differentiated from limiting flux(the “last” flux reachable). (see Bacchin, Patrice, Pierre Aimar, andRobert W. Field. “Critical and sustainable fluxes: theory, experiments,and applications.” Journal of membrane science 281, no. 1-2 (2006):42-69).

10 separate samples of the fibers made according to the abovemethodology were created and used to form 10 separate membranes. Themembranes were tested to establish their PWP and CWF. The membranesformed were tested for their PWP and CWF by:

Pure water flux experiments were performed using deionized water. Eachmodule was immersed in deionized water for 24 h, and run in the testsystem for 1½ h, to eliminate the effect of the residual glycerol on thehollow-fiber membranes before any sample collection. A UF experimentalunit designed to evaluate the PWP and protein rejection is shown indetail (Please see: C. S. Feng, B. Shi, G. Li, Y. Wu, Preparation andproperties of microporous membrane from polyvinylidene fluoridecotetrafluoroethylene) (F2.4) for membrane distillation, J. Membr. Sci.237 (2004) 15-24.). A transmembrane pressure of 1 bar and feed solutiontemperature of 20° C., all experiments were performed in hollow-fibermodules with crossflow mode. Two modules were prepared for eachhollow-fiber sample.

Pure water permeation fluxes (PWP) were obtained as follows:

When the pure water is passed through the membrane and readingscalculated using the equation above each value is tabulated and a graphbetween time and the readings is plotted. For the prolonged or extendedperiod of time (in our case more than 5 hours) the PWP value begins tostabilize signifying the CWF value for the membrane at this point. Theapparatus used for carrying out the PWP tests on the fibers can berepresented by the following schematic:

The results and essential conditions for the test are provided in Table1 below. The test was carried out at STP.

The table enlists the data recorded during for the PWP test performed onthe 10 hollow fiber membrane samples prepared.

TABLE 1 Flux Tables -5 pairs from 10 samples PakVitae's lab in SingaporeHF membrane flux summary Unit No Date 5 Mar. 2019 Inlet Pressure (bar) 11 1 1 1 Fiber ID Fiber-1 Flow Pattern OUT TO IN OUT TO IN OUT TO IN OUTTO IN OUT TO IN Number of Fibers 14 14 14 14 14 Length of Fibers (mm)180 180 180 180 180 ID (Reading

15 15 15 15 15 OD (Reading

25 25 25 25 25 ID (mm) 0.300 0.300 0.300 0.300 0.300 OD (mm) 0.500 0.5000.500 0.500 0.500 Area of fibers (m2) 0.00396 0.00396 0.00396 0.003960.00396 Total Duration Time (mins) 0 30 60 90 120 PUB water permeability(g/min) g/m 785 507 355 303 270 Times mins 5 5 5 5 5 PUB Water Flux(LMH-Bar) LMH 2380 1540 1080 920 820 Average Water FLux (LMH-Bar) 1350PakVitae's lab in Singapore HF membrane 2 flux summary Unit No Date 5Mar. 2019 Inlet Pressure (bar) 1 1 1 1 Fiber ID Fiber-2 Flow Pattern OUTTO IN OUT TO IN OUT TO IN OUT TO IN Number of Fibers 14 14 14 14 Lengthof Fibers (mm) 180 180 180 180 ID (Reading

15 15 15 15 OD (Reading

25 25 25 25 ID (mm) 0.300 0.300 0.300 0.300 OD (mm) 0.500 0.500 0.5000.500 Area of fibers (m2) 0.00396 0.00396 0.00396 0.00396 Total DurationTime (mins) 0 60 90 120 PUB water permeability (g/min) g/m 589 406 352308 Times mins 5 5 5 5 PUB Water Flux (LMH-Bar) LMH 1790 1290 1070 930Average Water FLux (LMH-Bar) 1360 PakVitae's lab in Singapore HFmembrane 3 flux summary Unit No Date 10 Mar. 2019 Inlet Pressure (bar) 11 1 1 1 Fiber ID Fiber-3 Flow Pattern OUT TO IN OUT TO IN OUT TO IN OUTTO IN OUT TO IN Number of fibers 14 14 14 14 14 Length of Fibers (mm)180 180 180 180 180

15 15 15 15 15

25 25 25 25 25 ID (mm) 0.300 0.300 0.300 0.300 0.300 OD (mm) 0.500 0.5000.500 0.500 0.500 Area of fibers (m2) 0.00396 0.00396 0.00396 0.003960.00396 Total Duration

0 30 60 90 120 PUB water

g/m 630 545 466 392 295 Times mins 5 5 5 5 5 PUB Water Flux

LMH 1910 1655 1415 1190 895 Average Water Flux (LMH-Bar) 1415 PakVitae'slab in Singapore HF membrane 4 flux summary Unit No Date 10 Mar. 2019Inlet Pressure (bar) 1 1 1 1 1 Fiber ID Fiber-6 Flow Pattern OUT TO INOUT TO IN OUT TO IN OUT TO IN OUT TO IN Number of fibers 14 14 14 14 14Length of Fibers (mm) 180 180 180 180 180

15 15 15 15 15

25 25 25 25 25 ID (mm) 0.300 0.300 0.300 0.300 0.300 OD (mm) 0.500 0.5000.500 0.500 0.500 Area of fibers (m2) 0.00396 0.00396 0.00396 0.003960.00396 Total Duration

0 30 60 90 120 PUB water

g/m 596 522 443 374 286 Times mins 5 5 5 5 5 PUB Water Flux

LMH 1810 1585 1345 1135 870 Average Water Flux (LMH-Bar) 1350 PakVitae'slab in Singapore HF membrane 5 flux summary Unit No Date 15 Mar. 2019Inlet Pressure (bar) 1 1 1 1 1 Fiber ID Fiber-5 Flow Pattern OUT TO INOUT TO IN OUT TO IN OUT TO IN OUT TO IN Number of Fibers 14 14 14 14 14Length of Fibers (mm) 180 180 180 180 180

15 15 15 15 15

25 25 25 25 25 ID (mm) 0.300 0.300 0.300 0.300 0.300 OD (mm) 0.500 0.5000.500 0.500 0.500 Area of fibers (m2) 0.00396 0.00396 0.00396 0.003960.00396 Total Duration

0 30 60 90 120 PUB Water

g/m 730 645 524 409 240 Times mins 5 5 5 5 5 PUB Water Flux

LMH 2235 1095 1590 1240 730 Average Water Flux (LMH-Bar) 1550 PakVitae'slab in Singapore HF membrane 6 flux summary Unit No Date 15 Mar. 2019Inlet Pressure (bar) 1 1 1 1 1 Fiber ID Fiber-6 Flow Pattern OUT TO INOUT TO IN OUT TO IN OUT TO IN OUT TO IN Number of Fibers 14 14 14 14 14Length of Fibers (mm) 180 180 180 180 180

15 15 15 15 15

25 25 25 25 25 ID (mm) 0.300 0.300 0.300 0.300 0.300 OD (mm) 0.500 0.5000.500 0.500 0.500 Area of fibers (m2) 0.00396 0.00396 0.00396 0.003960.00396 Total Duration

0 30 60 90 120 PUB Water

g/m 558 425 409 366 324 Times mins 5 5 5 5 5 PUB Water Flux

LMH 1815 1290 1240 1110 985 Average Water Flux (LMH-Bar) 1290 PakVitae'slab in Singapore HF membrane 7 flux summary Unit No Date 20 Mar. 2019Inlet Pressure (bar) 1 1 1 1 1 Fiber ID Fiber-7 Flow Pattern OUT TO INOUT TO IN OUT TO IN OUT TO IN OUT TO IN Number of Fibers 14 14 14 14 14Length of Fibers (mm) 180 180 180 180 180

15 15 15 15 15

25 25 25 25 25 ID (mm) 0.300 0.300 0.300 0.300 0.300 OD (mm) 0.500 0.5000.500 0.500 0.500 Area of fibers (m2) 0.00396 0.00396 0.00396 0.003960.00396 Total Duration

0 30 60 90 120 PUB water

g/m 643 518 416 372 312 Times mins 5 5 5 5 5 PUB Water Flux

LMH 1950 1570 1260 1130 945 Average Water Flux (LMH-Bar) 1370 PakVitae'slab in Singapore HF membrane 8 flux summary Unit No Date 20 Mar. 2019Inlet Pressure (bar) 1 1 1 1 1 Fiber ID Fiber-8 Flow Pattern OUT TO INOUT TO IN OUT TO IN OUT TO IN OUT TO IN Number of Fibers 14 14 14 14 14Length of Fibers (mm) 180 180 180 180 180

15 15 15 15 15

25 25 25 25 25 ID (mm) 0.300 0.300 0.300 0.300 0.300 OD (mm) 0.500 0.5000.500 0.500 0.500 Area of fibers (m2) 0.00.396 0.00396 0.00396 0.003960.00396 Total Duration

0 30 60 90 120 PUB water

g/m 707 556 416 326 251 Times mins 5 5 5 5 5 PUB Water Flux

LMH 2140 1690 1250 990 760 Average Water Flux (LMH-Bar) 1360 PakVitae'slab in Singapore HF membrane 9 flux summary Unit No Date 25 Mar. 2019Inlet Pressure (bar) 1 1 1 1 1 Fiber ID Fiber-9 Flow Pattern OUT TO INOUT TO IN OUT TO IN OUT TO IN OUT TO IN Number of Fibers 14 14 14 14 14Length of Fibers (mm) 180 180 180 180 180

15 15 15 15 15

25 25 25 25 25 ID (mm) 0.300 0.300 0.300 0.300 0.300 OD (mm) 0.500 0.5000.500 0.500 0.500 Area of fibers (m2) 0.00396 0.00396 0.00396 0.003960.00396 Total Duration

0 30 60 90 120 PUB water

g/m 784 406 354 303 275 Times mins 5 5 5 5 5 PUB Water Flux

LMH 2370 1230 1070 920 830 Average Water Flux (LMH-Bar) 1290 PakVitae'slab in Singapore HF membrane 10 flux summary Unit No Date 25 Mar. 2019Inlet Pressure (bar) 1 1 1 1 1 Fiber ID Fiber-10 Flow Pattern OUT TO INOUT TO IN OUT TO IN OUT TO IN OUT TO IN Number of Fibers 14 14 14 14 14Length of Fibers (mm) 180 180 180 180 180

15 15 15 15 15

25 25 25 25 25 ID (mm) 0.300 0.300 0.300 0.300 0.300 OD (mm) 0.500 0.5000.500 0.500 0.500 Area of fibers (m2) 0.00396 0.00396 0.00396 0.003960.00396 Total Duration

0 30 60 90 120 PUB water

g/m 674 515 364 305 292 Times mins 5 5 5 5 5 PUB Water Flux

LMH 2040 1560 1100 920 880 Average Water Flux (LMH-Bar) 1300

indicates data missing or illegible when filed

Table 2 provides a summary of the Pure Water Flux established over5-minute intervals over a 120 minute period for each of the membranes.The results are also charted in FIG. 8

TABLE 2 Sample-1 Sample-2 Sample-3 Sample-4 Sample-5 Sample-6 Sample-7Sample-8 Sample-9 Sample-10 LMH LMH LMH LMH LMH LMH LMH LMH LMH LMH 23801790 1910 1810 2215 1815 1950 2140 2370 2040 1540 1270 1655 1585 19551290 1570 1690 1230 1560 1080 1230 1415 1345 1590 1240 1260 1260 10701100 920 1070 1190 1135 1240 1110 1130 990 920 920 820 930 895 870 730985 945 760 830 890

Table 2 provides a summary of the Pure Water Flux established over5-minute intervals over a 120 minute period for each of the membranes.The results are also charted in FIG. 8

From these results, it can be seen that there is a good level ofconsistency across each of the samples. It can also be concluded thatthe initial PWP readings are higher as compared to the conventionalfibers, although over the prolonged testing the PWP readings tend todecline and stabilize at a point (where the graph tends to becomestraight and have a constant slope) which is designated as the CWF forthe respective membrane and CWF is the parameters which is used as thedesign factor when such membranes are used in their practicalapplications. However it can be seen that for all the samples the CWF isin the range of 800 to 900 Lmh, which again is an advantageous propertyof the fibers describes in the present invention, as it will requireless pressure to permeate the same amount of water through these fiberas compared to the conventional ones, hence saving costs.

Example 3: Testing for the Antimicrobial Nature of the Membrane FiberSurface

A membrane was provided with hollow fibers made according to Example 2,but with zinc salt embedded within the polymer. The principal polymerfor fiber making, in our case polyethersulfuone is modified using thesalts of Zinc such as Zinc Pyrithione and etc. The modification is donebased on the methods described in the U.S. Pat. No. 9,527,918.

The membrane was then tested for its ability to inhibit two types ofbacterial strains (Escherichia coli ATCC 8739 (Gram−) and Staphylococcusaureus 6538 (Gram+)) using the standard international method forevaluating the antibacterial of the polymer surfaces.

The results can be found in the images of bacterial cultures grown onthe Petri dishes and shown in the FIG. 9. The results are providedbelow.

TABLE 3 initial Control Spun Microbial inoculum inoculum polymericReduction Reduction Strains (cfu/ml) (cfu/ml) fiber log % EscherichiaColi  2.5 × 10⁶ Incubation 6.2 × 10⁷ 1.0 × 10⁴ 3.1 99.9 Staphylococcus|1.7 × 10⁶ at 37 2.5 × 10⁷ 1.4 × 10⁴ 2.9 99.9 degree Celsius for 24hours

The membrane was then tested for its ability to inhibit two types ofbacterial strains (Escherichia coli ATCC 8739 (Gram−) and Staphylococcusaureus 6538 (Gram+)) using the standard international method forevaluating the antibacterial of the polymer surfaces. The results can befound in the images of bacterial cultures grown on the Petri dishes andshown in the FIG. 9. The results are provided below.

As can be seen, the zone of inhibition for the tests carried out on thespun polymeric fiber (ie the polymer with zinc salt embedded therein)match the geometry of the fiber sample placed on the petri dish;representing an almost complete kill of the bacteria on the portions ofthe disk to which the fiber was applied. This is confirmed by the CFU/mlreduction presented in Table 3 for the initial inoculum compared to thatcalculated for the spun polymer fiber.

Test Method:

A hollow fiber obtained by spinning the antibacterial polymerPolyethersulfone prepared as described above was tested to evaluate theeffectiveness of the polymer against the main microbial strains definedby current legislation regarding plastic products intended to come intocontact with the skin.

The product was tested for 2 types of bacterial strains (Escherichiacoli ATCC 8739 (Gram−) and Staphylococcus aureus ATCC 6538 (Gram+))using the standard international method for evaluating the antibacterialactivity of non-porous plastic surfaces.

Moulded Initial Incubation Control polymer MICROBIAL inoculum at 37° C.inoculum item Reduction STRAINS (cfu/ml) for 24 h (cfu/ml) (cfu/ml) logReduction % Escherichia 2.5×10⁶ 6.2×10⁷ 1.0×10⁷ 0.79 83.87% coliStaphylococcus 1.7×10⁶ 2.3×10⁷ 1.4×10⁶ 1.2 93.91% Aureus

The initial bacterial suspensions were diluted so as to obtain a knownbacterial concentration expressed in colony forming units—cfu/ml. Thefibers analyzed were duly sectioned in order to produce pieces ofoptimal dimensions for conducting the tests. These were treated with thereference microbial strains, covered with sterile polyethylene film andplaced in an incubator at a temperature of 37±1° C. for 24 hours. At theend of the incubation period the samples were washed with neutralizingsolution, on which the residual microbial count was determined.

The results obtained show that after 24 hours of incubation at 37° C.the polymer treated with zinc reduces the bacterial count by 83.870 (inthe case of Escherichia coli) and 93.91% (in the case of Staphylococcusaureus).

FIG. 9. Explanation:

As can be seen from the figure that there are 6 petri dishes in total intwo sets of 3 each.

The 3 on top have a substance impregnated with silver Nano-particles togive the substance a biocidal property and the 3 below have the sampleextracted from the fiber surface of the present invention (spun hollowfiber membranes). It can be seen that the Nano-particles have leachedout in the above 3 petri dishes migrating/leaching out of the substanceto kill the bacteria around the sample. However the bacterial growth inthe lower 3 petri dishes is only inhibited at the surface if the samplewhich substantiates the claim that the substance responsible forimparting antimicrobial property does not leach out of the material ofthe present invention.

1.-44. (canceled)
 45. A process of making an intrinsicallyanti-microbial hollow fiber membrane comprising the steps of: I) a)mixing a polymer or a polymer mix with a pore former comprisingpolyethylene glycol (PEG); and b) passing the mixture produced in stepa) through a spinneret together with a non-solvent for the polymers; orcomprising the steps of; II) a) mixing an antimicrobial substanceembedded polymer or antimicrobial substance embedded polymer mix with apolymer or a polymer mix absent of an antimicrobial substance and with asolvent for both polymers; and b) passing the mixture produced in stepII) a) through a spinneret together with a nonsolvent for the polymers.46. A process according to claim 45, wherein: (i) step b) is carried outat a temperature of from 25 to 80° C.; and/or (ii) the spinneretoperates at a speed of from 350 rpm to 600 rpm.
 47. A process accordingto claim 45, wherein: (a) the antimicrobial substance is a metal oxide,metal salt or meta; and/or (b) the embedded polymer or polymer mix isfrom 2-5% by weight of total polymers in the mixture formed in step a).48. A process according to any of claim 45, wherein: (a) the polymer orpolymer mix with the anti-microbial substance and absent theanti-microbial substance is the same polymer or polymer mix; (b) theantimicrobial substance has metal oxide particles embedded thereinthrough cross-linking between polymeric chains; and/or (c) the processproduces intrinsically anti-microbial hollow fiber membranes comprisinga plurality of porous hollow membrane fibers wherein liquid enters fromoutside of the fiber membrane and passes through the porous membraneinto and along a lumen of the fibers, thereby retaining filtrate outsideof the membrane and filtered liquid flows out from a hollow end of thefiber.
 49. The process of making an intrinsically anti-microbial hollowfiber membrane according to claim 45, wherein: (a) the polymer or apolymer mix absent of an antimicrobial substance is from 95-98% byweight of the fiber; and/or (b) the antimicrobial substance embeddedpolymer is polyethersulfon and the polymer or a polymer mix absent of anantimicrobial substance is polyethersulfon, the polymers being providedin a 3% to 97% weight ratio.